Air concentration and bubble characteristics downstream of a chute aerator

Bai, Ruidi; Zhang, Faxing; Liu, Shanjun; Wang, Wei

doi:10.1016/j.ijmultiphaseflow.2016.07.007

Cited by 31 publications

(26 citation statements)

References 32 publications

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“…There are different proposals for energy dissipation mechanisms in open channel flows, depending on the regime analyzed. Turbulence and bubble effects play an important role in self-aerated open channels and stilling basins [13][14][15][16][17], but supercritical flows in spillways are highly influenced by roughness at the boundary [18]. The objective of the work presented in this article is to quantify the influence of aeration on the roughness boundary in high velocity and turbulent flows through friction mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Experimental Analysis of the Influence of Aeration in the Energy Dissipation of Supercritical Channel Flows

Rebollo

López

Garrote

et al. 2019

Water

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Energy dissipation structures play an important role in flood risk management. Many variables need to be considered for the design of these structures. Aeration has been one of the more studied phenomena over the last years, due to its influence in the performance of hydraulic structures. The purpose of the work presented in this article is to experimentally characterize the effects of aeration on boundary friction in supercritical and fully turbulent flows. The physical model used to analyze the aeration effects consists of a spillway chute 6.5 m high and a stilling basin of 10 m length and 2 m high. A pump and compressor supply the water-air mixture and are controlled at the entrance by valves and flowmeters. The ensuing channel is monitored to determine the velocity profile and air concentration of the flow into the stilling basin. The average values of both variables and Manning’s coefficient along the channel are used to determine the relation between air concentration and energy dissipation by friction. A velocity increase with greater air entrainment has been found in all scenarios since friction is the main energy dissipation mechanism in open channels flow. Finally, an equation is proposed to characterize this evolution based on the results obtained.

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Section: Introductionmentioning

confidence: 99%

Experimental Analysis of the Influence of Aeration in the Energy Dissipation of Supercritical Channel Flows

Rebollo

López

Garrote

et al. 2019

Water

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“…Hence, the Froude number F 0 (V 0 /(gh 0 ) 0.5 ) was within the range of 3.3 to 7.4 (Table 2), where g was the gravity. x was the streamwise coordinate along the chute bottom, h s was the offset height, L was the cavity length, and L m and L D were the specific lengths [9]. All measurements were performed on the channel centre line.…”

Section: Hydraulics Modelmentioning

confidence: 99%

“…For more than 25 experiments conducted in this model, only one set of experiments is shown herein to illustrate the basic chute aerator flow property [9]. However, equations presented hereafter are based on all experiments.…”

Section: Air Concentration and Bubble Frequency Profilesmentioning

confidence: 99%

“…Previous studies have provided a significant amount of information on the macroscopic air-water flow properties [2][3][4][5][6][7][8][9][10][11][12][13], such as the air concentration, air entrainment and detrainment. Rutschmann and Hager [2], combining both model and prototype data, proposed two approaches to calculate the air entrainment coefficient β = q a /q, where q a = air discharge and q = water discharge.…”

Section: Introductionmentioning

confidence: 99%

“…The authors also discussed the air entrainment and proposed two comprehensive methods to calculate the average and bottom air concentration development using deflectors and offsets along the chute. Avoiding the upper aeration effect, Bai et al [9] divided the chute aerator into three zones and found that an Many studies concerning the minimum or critical air concentration to avoid cavitation erosion have been conducted [18,19]. Peterka [18] found that when the average air concentration was between 0.01 and 0.06, no cavitation erosion was observed.…”

Section: Introductionmentioning

confidence: 99%

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Development of Bubble Characteristics on Chute Spillway Bottom

Bai¹,

Liu²,

Feng³

et al. 2018

Water

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Chute aerators introduce a large air discharge through air supply ducts to prevent cavitation erosion on spillways. There is not much information on the microcosmic air bubble characteristics near the chute bottom. This study was focused on examining the bottom air-water flow properties by performing a series of model tests that eliminated the upper aeration and illustrated the potential for bubble variation processes on the chute bottom. In comparison with the strong air detrainment in the impact zone, the bottom air bubble frequency decreased slightly. Observations showed that range of probability of the bubble chord length tended to decrease sharply in the impact zone and by a lesser extent in the equilibrium zone. A distinct mechanism to control the bubble size distribution, depending on bubble diameter, was proposed. For bubbles larger than about 1-2 mm, the bubble size distribution followed a-5/3 power-law scaling with diameter. Using the relationship between the local dissipation rate and bubble size, the bottom dissipation rate was found to increase along the chute bottom, and the corresponding Hinze scale showed a good agreement with the observations.

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